connection, even if it's something like a cell-phone signal. but other networks are more abstract, almost virtual: social networks, networks based on relationships of friendship; food webs, networks based on feeding relationships between species; markets and economies linked together by the flow of capital. in some sense, we could argue that everything on the planet, both living and inanimate, is part of one huge, beautiful, but complicated network. what do all these networks have in common? abstractly, they are comprised of intersections, or points, that we call nodes, or vertices, that are connected by lines, or paths, that we call edges. now, on this map, for example, cities are nodes and highways are edges. any real-life network can look very messy. in order to get to the heart of a network, mathematicians strip away all the particulars, leaving only the essence, the underlying mathematical graph.